Previous work from our laboratory has shown that morphine causes the release of an endogenous material into cerebrospinal fluid. Lower quantities of this material exist in the CSF of animals not given morphine. One of the principal objectives of our work in the future will be to identify the endogenous opiate like material. We also will determine whether other opiates such as methadone, meperidine and levorphanol as well as other agents which are active in the tail-flick test also cause a release of the endogenous material in CSF. The third objective of our future research will be to continue our investigations into the mechanism of antinociceptive actions of morphine in mice and rats. It is clear from data generated on this project that the antinociceptive action of morphine is mediated by different mechanisms in these two rodent species.